Measuring and maintaining the quality of water is important in a wide variety of circumstances. For example, for keeping fish and/or other aquatic life, the quality of the water must be kept within certain tolerances to keep the aquatic life healthy. As another example, the water in swimming and diving pools, hot tubs, and other sports, recreational, and therapeutic bodies of water need to be kept at certain levels of quality not only to maintain that water's clarity, but also to keep the users of these bodies of water safe from waterborne illnesses. As yet another example, the quality of potable water needs to be maintained within a range of tolerances as to a variety of chemical constituents for any one or more of a number of reasons, such as to make the water safe for ingesting, less harmful to distribution systems, and to promote healthfulness of the drinkers (e.g., in the case of adding fluorine and/or other nutrients). Those skilled in the art will readily appreciate that these are but a few examples of settings in which it is important to monitor and/or control the quality of water.